Computer systems typically utilize parallel power supply systems. A parallel power supply system generally comprises a plurality of power sources such as DC--DC converters or voltage regulators connected in parallel to provide current to a plurality of processors. FIG. 1a represents a typical parallel power supply configuration 10. This configuration 10 includes an input voltage 12, a fuse 14, a silicon controlled rectifier (SCR) 16, two VRMs 18, 20, a threshold voltage 22, a comparator 23, and a latch 24. FIG. 1b represents a typical VRM configuration 25 which includes first and second capacitors 26, 34, a transistor 28, a diode 30, an inductor 32, an output voltage 36, an error amplifier 37, a pulse width modulator 38, and a reference voltage 39. Typically, these types of parallel power systems do not include isolating diodes or transistors. However, a problem arises in these types of parallel power supply systems when one of the VRMs in parallel initiates an over voltage (OV) condition. When one 5 of the VRMs 18, 20 goes OV, it turns on the SCR 16 which can blow the fuse 14 and cause the entire system to shutdown. For a better understanding of this situation, FIG. 2 is a flowchart of the conventional VRM over-voltage protection scheme. Referring the FIG. 1a and FIG. 2 together, first, the output voltage of one of the VRMs 18, 20 exceeds the threshold voltage 22, via step 40. Next, the output of the latch 24 is driven high by the comparator 23, via step 42. Once the output of latch 24 is driven high, the SCR 16 is turned on, via step 44. Finally, once the SCR 16 is turned on, the fuse 14 will open and clear the fault, via step 46.
This scheme is generally implemented to protect the system against damage. However, the noisy conditions produced by the comparator 22 or an actual over voltage condition generated by VRM 18 or 20 can cause the blowing of the fuse 14. Once this happens, the VRMs will be without input power and the system will be forced to shut down and reboot. For many server and network application systems, this is not a desirable outcome.
Accordingly, what is needed is a circuit that can isolate the particular voltage regulator that is in an over voltage condition and shut it down. Also, the circuit should accomplish this without causing a shutdown of the entire system. The present invention addresses such a need.